Diabetes mellitus is a group of diseases causing abnormal blood sugar levels over a prolonged period of time. Diabetes is a result of either the pancreas not producing enough insulin, or the failure of the cells to respond to the insulin produced. As of November 2014, studies estimate that around 347 million people worldwide have the disease, Lancet, 378(9785):31-40 (2011). The World Health Organization (WHO) projects that diabetes will be the seventh leading cause of death by 2030.
Diabetes has been recognized since around 1500 BCE, but until only 50 years ago, accurate glucose monitoring required individuals to visit healthcare professionals. As management of the disease focuses on monitoring of glucose and finding a lifestyle that better controls glucose levels, visiting a doctor's office for every test is inefficient and ineffective. More accurate monitoring systems were developed in the 1960's, allowing individuals to test at home. Since that time, glucose monitors have improved from biochemical reactions in which a color change would be visually compared to a color chart, to electrochemical reactions in which a reaction with the glucose in the blood would be measured and read digitally. In the last 50 years, tests have gotten faster (from over a minute to just a few seconds) and easier (early tests required washing and blotting test strips), and lancets have evolved from steel strips with a point to spring-loaded needles. These changes have made home testing better, but the fact remains that drawing blood for testing is not only a potential health hazard, but also carries with it social stigma, pain, produces medical waste that needs proper disposal, and the patient has to bear the cost of one time use test strips.
Research has focused on a non-invasive or minimally invasive monitoring system since at least the mid 1970's. These systems have approached the problem through numerous medical monitoring techniques, each presenting its own set of drawbacks
U.S. Pat. No. 8,743,355, (the '355 Patent), entitled “Simple Sugar Concentration Sensor and Method,” issued Jun. 3, 2014, which is hereby incorporated by reference herein in its entirety, discloses optical sensing of the angular rotation of optical energy passed through a sample including a sugar, for example, glucose in a fluid. In particular the '355 Patent discloses using photosensitive detectors to sense the rotation of polarized light that passes through a sample, for example, through human tissue including blood. As described in the '355 Patent, the angular rotation of the optical energy passing through a sugar containing solution is described by the relation:Θ=∝×L×C   (Equation 1)
Where L is a path length, C is the sugar concentration in the fluid, and α is a rotation constant. The constant α depends on the wavelength of the light, the type of sugar molecule, and the fluid in which the sugar is dissolved.
The '355 Patent describes optical measurements made on a portion of the human ear using polarizers to create polarized light, and a difference measurement taken between two photosensitive detectors, one with a polarizer, and one without. However, using the prior known approaches that are described in the '355 Patent, the readings obtained require additional accuracy and an increase in reproducibility to enable a practical glucose meter for patient use.
The inventors of the present application have further researched the approach of the '355 Patent and related non-invasive glucose measurements and found that the prior known approaches described to date lack the accuracy, reproducibility in results, efficiency and ease of use needed to provide a practical commercial non-invasive glucose monitor.
Improvements are therefore needed in non-invasive glucose monitoring in order to address the deficiencies and the disadvantages of the prior known approaches. Solutions are needed that reduce the cost and complexity of the monitor system and which can accurately measure changes in blood glucose concentration.